scottmcgurk Posted December 16, 2013 Share Posted December 16, 2013 Morning guys, Having a small issue with non-firing pyro which I cant seem to quite get my head around.We are firing 6 LeMaitre Silver Jets (Reduced Height) in two fans of three. These fans are wired in parallel. Each fan has its own firing channel on the rail - we'll say F2 & F3 for example sake. F2 is placed on stage, and connected to the rail via shooting wire (closest to 24WG I'd say) with a length of about 4m to the rail.F3 is placed on the other stage side, again connected to the rail with shooting wire, but this time with a length of around 12-15m. Upon firing fan F2 always fires completely. Fan F3 however has been giving issues, in some cases 1/3 firing, some cases non-fire, however the controller still sees continuity on the fan.Have tried with two different sets of jets - same results. My thoughts are that the parallel loading is potentially dropping the firing power on that circuit due to the relative thin guage wiring that is there?Can someone shed any light on potential causes for this behaviour? Cheers Link to comment Share on other sites More sharing options...
timsabre Posted December 16, 2013 Share Posted December 16, 2013 When firing multiple pyro on one channel, you wire them in series. Sounds completely wrong but it works. Otherwise as you have experienced, there is often not enough power to fire all the devices. (Learned this the hard way doing a balloon reveal with about 20 microdets wired in parallel - pressed the button - nothing happened at all... later testing proved the "wire in series" method to be correct) Link to comment Share on other sites More sharing options...
d_korman Posted December 16, 2013 Share Posted December 16, 2013 When firing multiple pyro on one channel, you wire them in series. Sounds completely wrong but it works. Otherwise as you have experienced, there is often not enough power to fire all the devices. (Learned this the hard way doing a balloon reveal with about 20 microdets wired in parallel - pressed the button - nothing happened at all... later testing proved the "wire in series" method to be correct) Though if you are connecting different types (or makes) in series, sometimes one type will fire too quickly and break the firing circuit before the other matches have ignited. It doesn't happen often, but it's happened to me (though that was some time ago when, IIRC, Le Maitre changed the type of match they were using and we had some of each type - I think the new ones were faster). If that happens it's better to use seperate circuits for the different types (though still wire in series within each type). Link to comment Share on other sites More sharing options...
scottmcgurk Posted December 16, 2013 Author Share Posted December 16, 2013 d_korman, that may well explain what I have written below!Yes, I know the wire in series method well - but have had experiences in the past with series wiring that one effect will fire and pop the circuit for the others.May as well give the series wiring method a try - I guess it wont work any worse that it does at present! Just seems bizarre that an extra 10m of cable would make the odds (unless of course I am right on the limit for the controller as it stands!) Link to comment Share on other sites More sharing options...
Brian Posted December 16, 2013 Share Posted December 16, 2013 What you are describing is exactly what I'd expect from using parallel wiring. Here's an example what I did some while ago, the 1.6R resistors are the igniters, the 0.25R resistors are the wring and connections... ...notice how igniter R18 is marginal for firing being only just about 500mA, R21 is even more marginal being closer to the 300mA 'no-fire' current than the 500mA 'fire' current, and R24 won't fire. Also notice the magnitude of the firing current. Unless you have a particularly beefy firing unit, it isn't going to deliver 20 Amps. Link to comment Share on other sites More sharing options...
timsabre Posted December 16, 2013 Share Posted December 16, 2013 I never tried firing different devices on one circuit, that's interesting to know. What's the controller, normal pyroflash? 10m of weedy cable has a significant resistance... Link to comment Share on other sites More sharing options...
Brian Posted December 16, 2013 Share Posted December 16, 2013 If that happens it's better to use seperate circuits for the different types (though still wire in series within each type).If your controller has a reasonable output current you can get away with wiring all identical igniter types in series strings and then the two series string in parallel. Link to comment Share on other sites More sharing options...
scottmcgurk Posted December 16, 2013 Author Share Posted December 16, 2013 Indeed - many thanks Brian. I'm aware of the differences in series / parallel circuit wiring but seeing it like that covers it much better.I looped the cable last night and did a test on the resistance of the firing line - seems to come in about a few ohms (I say about, a well meaning tech had borrowed my digital meter and not returned it). Controller in use for this show is a pyrosure - according to specs is rated at up to 80amp@30V . I guess the devil here is in the *up to* part!! Link to comment Share on other sites More sharing options...
bigclive Posted December 16, 2013 Share Posted December 16, 2013 The resistance of the cable will be quite significant for such a low load with the matches wired in parallel. Each match has a typical resistance of about 1 or 2 ohms and when you wire them in parallel the resistance is likely to be lower than the cable feeding them and even a fraction of an ohm resistance in a connector or twisted connection will have a significant impact on the maximum trigger current that can flow and where it is dissipated. The matches each require about 1A to fire so putting them in parallel adds up to quite a current requirement. Wiring arrays of pyro effects in series does seem to defy electrical logic on the basis that the first to fire will break the circuit, but it works. I'm not sure the exact mechanism. It's either that the ignitor wires all get up to combustion temperature before one breaks, or perhaps the explosive plasma surrounding each successful detonation effectively bridges the circuit momentarily. As the others mention, it's a good idea to ensure pyro is all from the same batch in each series string to ensure reliable ignition. Link to comment Share on other sites More sharing options...
scottmcgurk Posted December 16, 2013 Author Share Posted December 16, 2013 Cheers bigclive - are you the same bigclive from the big clive website perchance? Ok - I had a sneaking suspicion it was the current that was causing the dropout! I'll switch them over to series and see where it goes.... I do agree though, series does seem to defy logic slightly, but then have past experience of it working as well!! Link to comment Share on other sites More sharing options...
Brian Posted December 17, 2013 Share Posted December 17, 2013 I'm not sure the exact mechanism. A bit of magic and a lot of the Adiabatic process. Link to comment Share on other sites More sharing options...
bigclive Posted December 17, 2013 Share Posted December 17, 2013 Cheers bigclive - are you the same bigclive from the big clive website perchance? It sure is. By the way, that Adiabatic process thing is quite mind numbing to read about. Wiki on Adiabatic process. Link to comment Share on other sites More sharing options...
paulears Posted December 17, 2013 Share Posted December 17, 2013 I'm solo glad you said that Clive. I read it about four times and still had a numb brain, and thought it was just me! Link to comment Share on other sites More sharing options...
bruce Posted December 17, 2013 Share Posted December 17, 2013 Oh, Brian, why did you have to post that! It's made me realise just how much about thermodynamics I've forgotten.... Link to comment Share on other sites More sharing options...
boatman Posted December 17, 2013 Share Posted December 17, 2013 ..Wiring arrays of pyro effects in series does seem to defy electrical logic on the basis that the first to fire will break the circuit, but it works. I'm not sure the exact mechanism. .. I know nothing of pyro, but Ohms law shows that if four igniters are connected in series across 24V, a 5R6 resistor connected across each one would ensure a minimum of 1.1A would always flow in the circuit (assuming the last igniter to fire has a resistance of 2 Ohms). Then all the igniters would eventually fire. Left connected the resistors would dissipate about 7W each. Obviously, for a different number of igniters in the series the resistor values would need to change. Am I being a little naive or is that a practical "sure-fire" solution? Link to comment Share on other sites More sharing options...
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